Added test stubs for GPG Keys.

Added test stubs for GPG Keys tests for UI/CLI. These will have to be
written out following the information provided in the doctstrings.

``IMPORTANT``: Searching by `name` in the CLI is currently not working
but it shouldn't prevent us from writing the tests.

```bash
$ hammer gpg --help
Usage:
    hammer gpg [OPTIONS] SUBCOMMAND [ARG] ...

Parameters:
    SUBCOMMAND                    subcommand
    [ARG] ...                     subcommand arguments

Subcommands:
    list                          List GPG Keys
    info                          Show a GPG key
    create                        Create a GPG Key
    update                        Update a GPG Key
    delete                        Destroy a GPG Key

Options:
    -h, --help                    print help

$ hammer gpg create --help
Usage:
    hammer gpg create [OPTIONS]

Options:
    --organization-id ORGANIZATION_ID organization identifier
    --name NAME                   identifier of the GPG Key
    --key GPG_KEY_FILE            GPG Key file
    -h, --help                    print help

$ hammer gpg list  --help
Usage:
    hammer gpg list [OPTIONS]

Options:
    --organization-id ORGANIZATION_ID organization identifier
    --search SEARCH               Search string
    --page PAGE                   Page number, starting at 1
    --per-page PER_PAGE           Number of results per page to return
    --order ORDER                 Sort field and order, eg. ‘name DESC’
    --full-results FULL_RESULTS   Whether or not to show all results
    --by BY                       Field to sort the results on
    --order ORDER                 How to order the sorted results (e.g. ASC for ascending)
    -h, --help                    print help

$ hammer gpg info  --help
Usage:
    hammer gpg info [OPTIONS]

Options:
    --id ID                       resource id
    --name NAME                   resource name
    -h, --help                    print help
```
Merge pull request #338 from omaciel/cli-gpg-tests

Added test stubs for GPG Keys.